1. Field of the Invention
The present invention relates generally to a color illuminating system that illuminates color light beams by separating them from white light emitted from a light source and a projection type image display apparatus using the color illuminating system. More particularly, the invention is directed to a color illuminating system that illuminates high-efficiency color light and minimizes the overall optical system size, and a projection type image display apparatus using the color illuminating system.
2. Description of the Related Art
In general, projection type image display apparatuses form images by projecting images generated by a micro-display system, such as a liquid crystal display or a digital micro-mirror display, on a screen by means of a light source.
Such projection type image display apparatuses may be classified into 1-panel type displays and 3-panel type displays depending on the number of micro-displays used. A 3-panel, projection type image display that utilizes three micro-displays arranged in the optical paths of separate red, blue, and green light beams ensures higher light efficiency but is structurally complicated and has a higher manufacturing cost.
A basic 1-panel, projection type image display apparatus can periodically isolate red, green, and blue light beams from incident white light with a simple structure using a color wheel. However, this type of device has poor light efficiency due to the use of the color wheel, which leads to loss of two thirds of the incident light. Thus, there has been manufactured 1-panel, projection type image display apparatuses in consideration of such light efficiency reduction.
An example of a conventional 1-panel, projection type image display apparatus is illustrated in FIG. 1. In the conventional 1-panel, projection type image display apparatus, non-polarized white light is generated and emitted by a light source 11. The emitted white light is made uniform while passing a fly-eye lens array 13 and is directed towards a polarizer 15. The polarizer 15 polarizes the non-polarized white light emitted from the light source 11 into white light having a predetermined polarization component. The white light passed through the polarizer 15 is split into red, blue, and green light beams by first and second dichroic lenses 17 and 19. The first dichroic lens 17 reflects light of a blue wavelength among the incident white light and transmits light of the other wavelengths. The light transmitted through the first dichroic lens 17 is split into green and red light beams by the second dichroic lens 19.
First, second, and third scanning prisms 21, 23, and 25 that periodically scroll incident light are disposed in the optical paths of the split color light beams. The first, second, and third scanning prisms 21, 23, and 25 have a rectangular prism and are turned by a driver (not shown). As the first, second, and third scanning prisms 21, 23, and 25 are turned, the angle of a side wall of each of the first, second, and third prisms 21, 23, and 25 to the optical axis is altered. The optical paths of the light passed through each of the first, second, and third scanning prisms 21, 23, and 25 is periodically altered.
When turning the first, second, and third scanning prisms 21, 23, and 25, an initial angle of rotation of each of the first, second, and third scanning prisms 21, 23, and 25 is set such that an effective image region of a display 33 is evenly divided by the lights passed through the first, second, and third scanning prisms 21, 23, and 25. As the first, second, and third scanning prisms 21, 23, and 25 are turned, sets of colored light beams (B, R, G), (G, B, R), and (R, G, B) alternately enter the effective image region of the display 33.
The light beams passed through the first and second scanning prisms 21 and 23 are combined together by a third dichroic mirror 27 and then combined with the light beam passed through the third scanning prism 25 by a fourth dichroic mirror 29. A reflecting mirror 18 is disposed between the first and third dichroic mirrors 17 and 27, and a reflecting mirror 20 is disposed between the second and fourth dichroic mirrors 19 and 29 to alter the paths of light.
The scrolling light that passes the fourth dichroic mirror 29 enters a polarizing beam splitter 31 that transmits or reflects the incident light depending on the polarization of the incident light. Light reflected by the polarizing beam splitter 31 is periodically scrolled such that sets of color light beams as illustrated in FIG. 2 alternately enter the display 33. The display 33 forms images from the incident light. The images are formed by changing the polarization of light to be output in units of a pixel. Only the light whose polarization component was altered after being incident on the display 33 is allowed to transmit the polarizing beam splitter 31 and go toward a projection lens unit 35. The projection lens unit 35 magnifies and projects the received images on a screen 50.
The projection type image display apparatus includes a plurality of relay lenses 41 through 48 disposed in optical paths to guide the light from the light source 11 up to the display 33.
Even though the above conventional projection type image display apparatus includes only one display to form color images, its optical structure is complicated. In addition, the three scanning prisms are separately turned for scrolling and it is difficult to synchronize them by driving the display.